Glass-reinforced thermoplastic engineering resins are known to exhibit excellent mechanical strength and tensile properties. As a consequence, glass-reinforced thermoplastic engineering resins are traditionally used to form various components in a number of end-use applications (e.g., parts for electrical and electronic apparatus, automotive parts, and the like).
Molded parts formed of such glass-reinforced thermoplastic engineering resins are sometimes visible and/or used for ornamental purposes. For these reasons, it may be desirable to impart a particular color characteristic to the resin by incorporating pigmenting agents. In this connection, a number of dyes and pigments have been used so as to impart desired color characteristics to resin compositions. However, it is typically necessary to use a white pigment, either alone so as to impart whiteness to the resin composition or conjointly with a non-white color pigment so as to impart a softer color tone and/or a desired opacity to the resin composition. In general, titanium oxide has been employed as a white pigmenting agent for such purposed in conventional thermoplastic resin compositions.
When titanium oxide is employed as a white pigmenting agent, for example, in glass-reinforced polyester resin compositions, its presence typically causes mechanical property deterioration (e.g., decreases in tensile elongation and/or impact shock resistance). In addition, molded articles formed of a resin which includes titanium oxide as a white pigmenting agent may not entirely be satisfactory in terms of appearance, color tone and/or whiteness. As a result, the end-use applications for such titanium oxide pigmented resins is considerably restricted.
Various inorganic materials, for example carbonates, sulfides and metal oxides other than titanium oxide, have been employed in an attempt to impart the desired whiteness to resin compositions. However, since most of these other inorganic materials which have been used as a white pigmenting agent possess a refractive index that is approximately the same as the resin, they generally do not impart the desired white opacity to the resin. For those inorganic materials which do exhibit a desirable whiteness effect, they typically must be added in greater amounts as compared to the amounts needed to obtain comparable whiteness when titanium oxide is used. Excessive use of such inorganic materials thus tends to exacerbate mechanical property deterioration, degrade the surface effects on molded parts and the like.
What has been needed in the art, therefore, are improvements regarding imparting white pigmentation to normally solid thermoplastic engineering resin compositions without deleteriously affecting their mechanical properties. It is towards providing such a need that the present invention is directed.
Broadly, the present invention resides in the discovery that satisfactory whiteness for thermoplastic engineering resins may be achieved by incorporating (blending) the anatase form of titanium dioxide (i.e., octahedrite) in a thermoplastic base resin. The effects of the present invention are especially evident when the base resin includes a glass reinforcement medium (e.g., glass fibers, beads, flakes, powders, etcetera).
In preferred forms, the present invention will be embodied in a thermoplastic resin composition having between 0.01 to 10 parts by weight of the anatase form of titanium dioxide which is blended with 100 parts by weight of a glass-reinforced thermoplastic resin composition. The glass-reinforced thermoplastic resin composition will itself be comprised of between about 35 to 95 parts by weight of a thermoplastic base resin (e.g., polyacetal, polyester, polycarbonate, polyphenylene sulfide and the like), and between about 5 to 65 parts by weight of a glass filler material as a reinforcement agent.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.